conventional exhaust emission reduction apparatus is designed to trap and burn or to control exhaust emission in an exhaust pipe using a filter, for instance, of ceramic or catalyst, but it has difficulty in obtaining a high removal performance of the harmful particulate matter due to an excessive pressure loss in compliance with its use, re-emission of the harmful particulate matter from the filter, and the like.
FIG. 1 illustrates a conventional exhaust emission reduction apparatus. This exhaust emission reduction apparatus includes a porous filter 114 installed in the tailpipe 112 of a vehicle. The exhaust gas emitted from an engine passes through the porous filter 114, and harmful substances contained in the exhaust gas are adsorbed to the porous filter 114. Thereby, the exhaust gas is cleaned. With the use of this filter 114, the clogging of the filter 114 causes the increase of a pressure loss.
In order to remove the harmful particulate matter trapped by the filter 114, the harmful particulate matter should be burned or dusted off. When the harmful particulate matter is burned, the sequential combustion process should be employed. Furthermore, during heating, the volume of the filter 114 increases and it leads to the break in the filter 114.
Further, in the combustion process, the filter 114 encounters various problems in that its lifespan maybe reduced by the shock of heat, and that its function is deteriorated by incomplete combustion.
This conventional exhaust emission reduction apparatus has a problem in that fine particles are emitted again from the filter 114 while the filler 114 is regenerated by a method such as combustion, and another problem in that other harmful gases or particulate matters are generated by secondary reaction.
Furthermore, an exhaust emission reduction apparatus based on an electrostatic precipitator mechanism has a problem in that, because the electric resistivity of the harmful particulate matter is low, the harmful particulate matter is attached to a dust collecting plate and then detached again from the plate. A device for continuously removing the trapped harmful particulate matter is additionally required.
Further, when the harmful particulate matter is trapped by an electrostatic precipitator, a phenomenon where the harmful particulate matter is repetitively trapped at a tip of the trapped harmful particulate matter, thereby growing in a shape similar to a chain, so-called a pearl chain phenomenon, takes place. As a result, an electric field between a ground electrode and a discharge electrode is disturbed. Thereby, the dust collection efficiency is reduced.